This invention relates to linear polymer beads containing repeating units of vinylbenzyl alcohol, thereby having the capability of forming thermally crosslinked resin beads. The invention further relates to such thermally crosslinked beads, methods of preparation, and various uses of the beads including use as adsorbents and as intermediates in the preparation of ion exchange resins.
Resin beads intended for ion exchange and related uses are conventionally crosslinked during the preparation thereof to an extent depending upon the degree of swelling and density desired in the product. For example, ion exchange resins which have been synthesized with low levels of crosslinker are less dense than those which have been made with high levels of crosslinking material. The extent of crosslinking, and therefore swelling and density, controls the selectivity of the resin with respect to species to be adsorbed or exchanged. Crosslinking is evidenced by decreased solubility and decreased swelling of the polymers in solvents.
Commonly, polymers are crosslinked during bead formation by copolymerizing a monoethylenically unsaturated compound with a polyethylenically unsaturated compound, such as the copolymerization of styrene with divinylbenzene. This represents a form of primary crosslinking. Further crosslinking may take place during treatment of a linear polymer to incorporate active sites (to which can be attached ion exchange functional groups), such as occurs upon chloromethylation of styrene polymers or copolymers. The latter form of crosslinking is often termed "secondary crosslinking." Polymer beads may be post-crosslinked by copolymerizing two monoethylenically unsaturated compounds, one of which also contains a group capable of crosslinking by condensation, and then treating with a suitable reagent for reacting with such group. Alternatively, a linear polymer may be formed from a monomer already containing an active site for attachment of an ion exchange group, by reaction under polymerization conditions with a polyfunctional crosslinking agent. U.S. Pat. No. 3,843,566 describes products of the last type, including polyvinylbenzyl chloride crosslinked with divinylbenzene as an intermediate in the preparation of macroreticular (macroporous) ion exchange resins. Such product has the advantage over chloromethylated styrene polymers of substantial absence of secondary crosslinking. Attempts have been made to avoid the use of added crosslinking agents by thermally crosslinking polymers containing at least 38 mole percent of alkyl vinyl aromatic hydrocarbons by heating at temperatures between 240.degree. C. and 260.degree. C. for a time between 8 hours and 7 days in the presence of an inert gas. See U.S. Pat. No. 2,987,508.
All of the foregoing crosslinking procedures require steps or other process conditions which complicate the formation of the crosslinked resin bead, either by virtue of need for an added crosslinking agent or by extreme temperature requirements. Such procedure also place limitations on total utilization of all reactants and resin bead properties, such as size uniformity, swelling, and product use.